The subject matter disclosed herein relates generally to power supplies, and more particularly to a driver device for supplying power to a laser.
Optical communication systems typically utilize semiconductor diodes or lasers as the transmitter. An example of such a device is a vertical cavity surface emitting laser (VCSEL). Semiconductor lasers, including VCSELs, are operated above a threshold level which requires that a bias be applied to the device in order to maintain the laser in a lasing mode. In the lasing mode, a modulating signal is applied to the device centered about a set modulation current. This provides a modulated optical output signal.
Conventional driver circuits utilize both P-channel and N-channel devices to supply the modulating signal and the modulation current. For example, assume that the VCSEL is operational between a first power setting, wherein the VCSEL is lasing but at a reduced power level, and a second power setting, where the VCSEL is lasing at an increased power level. When the VCSEL is operated at the increased power setting, the P-channel device provides the maximum current to the VCSEL. However, when the VCSEL is operated at the reduced power level, the N-channel device steers a portion of the current to ground. As a result, a slower P-channel device is utilized to provide a constant current to enable the VCSEL to operate at the increased power level and the N-channel device is utilized to steer a portion of the current away from the VCSEL when the VCSEL is operated at the reduced power level.
As a result, the P-channel device generates the same relatively high current regardless of the operational mode of the VCSEL, thus increasing the power required to operate the VCSEL. Moreover, because the P-channel device is always active, the power dissipated by the VCSEL is relatively high. As communication systems become more complex and the quantity of VCSELs increase, the power consumption of the communication system also increases.
Therefore, a need remains for a VCSEL driver that is capable of operating at increased speeds while also supplying a modulated current to the VCSEL in a more energy efficient manner.